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Fuel Injection - What are Your Thoughts ?
Fuel Injection - should I want that ? Why or why not ?
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Fuel Injection
Fuel injection on a four cylinder Lycoming can result in as much as 1 gallon/hour less fuel consumption than a carburetor. Exactly how much depends on the intake system and carb.
Fuel distribution is much better on injected engine allowing better leaning and loan of peak operation. Many carbs do not permit lean of peak, some do. |
Costs
If you were buying new, a carb. used to be much cheaper than fuel injection. With experimental FI systems now available the extra cost difference for FI is getting smaller.
The no core price for a rebuilt MA-4-5 carb is $1800...:eek: http://www.aircraftspruce.com/catalo...elyccarbs1.php |
No carb ice.
When I built my engine (2007) at a Superior build school, the price differential was only a few hundred dollars, so well worth the cost at that time. Assuming I'm saving 1/2 gallon/hour by running LOP, so far I've saved 350 gallons x $3.00/gallon (very conservative fuel cost estimate) or north of $1000. YMMV. Greg |
I have flown several carb'ed RVs and the #1 issue I always see is un-even fuel distribution as displayed by a 4 point CHT / EGT indication system, especially at partial throttle. Usually at W/O throttle the CHT/ EGT split is fairly even, anything less than that may cause a "front / rear" split. The 1/2 cylinders can run as much 300 deg cooler EGT than the 3/4 cylinders, which run hot anyway, at certain throttle plate positions. One has to wonder how healthy that is for the engine and how much power is being made in such a condition. The issue of O-360 sumps on O-320 engines and the corresponding lip just above the carb may also contribute to the un-even fuel distribution. With a carb, the fuel is introduced at one central point, the carb. Irregularities in the induction system can result in un-even flow. With F/I, the fuel is injected directly at the cylinder, resulting in very consistent CHT/EGT and the ability to run LOP. I have been very happy with the AFP FM series of F/I units. Once you understand the purge valve, hot starts are simple and reliable. No carb ice issues and the ability to pull sustained negative G are also in favor of the F/I system. Initial build cost and simplicity of installation seem to favor the Carb, but the long term fuel efficiency and safety (carb ice) seem to favor the F/I system.
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I opted for Don Rivera's Airflow Performance FM-150, my first ever fuel injected Lycoming. I'm not having any starting problems commonly attributed to mechanical fuel injected aircraft, and the way it operates when running is better in every regard.
I did operate a Mazda Rotary engine in my RV-8 for a while, the automotive style electronic injection has a lot going for it. Simple Digital Systems, and EFII are 2 examples. My son Peter installed a Rotec TBI in his RV-4 so he could fly upside down. It's often called an injector, but I call it a Diaphram Demand carb. It runs very well, and in our case has very even fuel distribution. I don't reject any of these fuel systems, even the Marvel carb has benefits. But I am happy with the FM-150 and will stick with it. |
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Back to the question; the carb is simple. Which is what I like most about it. Sure, I would like to have FI, but thinking through that installation, plumbing, electrical etc. was time/money I chose to avoid. Still like the simplicity of the carb. Fires up every time, no primer installed either. |
Aerobatics?
FI runs in any orientation. A carbureted engine will quit under zero or negative G operation. This makes the choice simple for me. YMMV.
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I elected for Fuel Injection from the get-go when ordering my engine. It was one of the best decisions I made (... right along with the LSEI ignition on the R. side.) I would not change that decision under any circumstance. There's nothing complicated about the Bendix-style injection, and as others said, it will let you run LOP and save significant fuel over the life of the aircraft. In my case, the difference between running 50 degrees LOP and 75 degrees ROP is 20% fuel savings. Nothing to sneeze at. :) The FI pays for itself pretty quickly.
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